Electrophotographic apparatus with synchronized document illumination and scanning feature

ABSTRACT

The optical illumination and scanning system for document reproduction consists of two rotatable mirrors mounted in fixed side-by-side relationship. A light source illuminates the first mirror which reflects the light to a section of an original document. This light is reflected by the document to the second mirror which reflects this return beam through a lens system to a photoconductor surface. The mirror assembly oscillates across the entire original without changing the fixed relationship between the light beam reflected to the original and the return beam focused on the photoconductive surface.

ilnited States Patent 1 Bruce et al.

[111 3,720,465 M lMarch 13, 1973 l ELECTROPHOTOGRAPHlC APPARATUS WITHSYNCHRONIZED DOCUMENT ILLUMINATHON AND SCANNING FEATURE [75] Inventors:George D. Bruce; Ronald V. Davidge; Raymond L. Fowler; George W.llobgood, Jr.; Henry C. Locklar, Jr.; George W. Van Cleave, all ofLexington, Ky.

[73] Assignee: International Business Machines Corporation, Armonk, N.Y.

[22] Filed: Nov. 20, 1970 [21] Appl. No.: 91,447

[52] [1.8. CI. "355/8, 355/47, 355/66 [51] Int. Cl. ..G03g 15/04 [58]Field of Search ..355/47, 8, 65, 66; 95/l2.5

[56] References Cited UNITED STATES PATENTS 2,600,168 6/1952 Klyce..95/45 Tiger at al. ..355/8 Brueggeman ..355/47 Primary Examiner-JohnM. Horan Atl0rneyHanifin and Jancin and D. Kendall Cooper [57] ABSTRACTThe optical illumination and scanning system for document reproductionconsists of two rotatable mirrors mounted in fixed side-by-siderelationship. A light source illuminates the first mirror which reflectsthe light to a section of an original document. This light is reflectedby the document to the second mirror which reflects this return beamthrough a lens system to a photoconductor surface. The mirror assemblyoscillates across the entire original without changing the fixedrelationship between the light beam reflected to the original and thereturn beam focused on the photoconductive surface.

2 Claims, 9 Drawing Figures YPATENTEDHAR 1 3191s SHEET 10? e GEORGE D.BRUGE RONALD V. DAVIDGE RAYMOND L. FOWLER GEORGE W. HOBGOOD, JR.

HENRY G. LOCKLAR, JR.

GEORGE W. VANGLEAVE WQM 0.

ATTORNEY.

PATENIEEMAR 1 3197s I SHEEF 20F 6 FIG. 3

PATENTEDHARI 3197s SHEET 3 OF 6 FIG.6

PATENIEUMAM 3mm SllELl 5 UI' FIG. 8

PATENTEUHAR] 3l973 1 0,1155

SHEET 6 OF 6 ELECTROPIIOTOGRAPHIC APPARATUS WITII SYNCIIRONIZED DOCUMENTILLUMINATION AND SCANNING FEATURE BACKGROUND OF INVENTION AND PRIOR ARTThe following U. S. Pat. Nos. are representative of the prior art:2,508,650 3,072,798 3,184,847 3,205,367 3,360,659.

Other art of interest in U. S. Pat. No. 3,345,926 which shows aparabolic reflector 42 to focus the light source and scanning mirror 43which directs the light source across the original and to thephotoconductive surface. U. S. Pat. No. 3,062,109 shows a light shieldused in conjunction with moving lamps in a photocopying device forkeeping stray light from the source of illumination; U. S. Pat. No.3,364,816 shows the use of an elliptical mirror to focus light. U. S.Pat. No. 3,995,066 discusses the theory of anamorphotic system whichincludes mirrors and '30 in FIG. 5 oscillating in synchronism.

U. S. Pat. No. 3,062,109 is representative of prior illumination andscanning systems. A- scanning mirror is pivoted on an axis and rotatesthrough an angle to scan a document placed atop a curved glass platen.The image of the document is projected onto a photoconductor drum by.means of a lens assembly and stationary mirror. An aperture defines thewidth of the document area that is scanned. Twelve fluorescent apertureSUMMARY OF THE INVENTION In accordance with the present invention,electrophotographic apparatus is provided with illumination and opticalscanning and projecting facilities that illuminate only a portion of thedocument as it is being scanned during operation. In a typical case,only 1/ 10 of the total area of the original document is actuallyilluminated, thereby enabling a significant reduction in the amount ofillumination required in the system. To achieve this, the illuminationsource comprises an elliptical reflecting means which concentrates thelight rays from the source to a linear confined area with relativelyhigher intensity than in prior systems. Reflector means are positionedin a manner to reflect the light rays from the light source to theoriginal document, to thereafter receive reflected light from thedocument and convey the same through the projection facilities of thesystem to image the photoconductor surface. In a preferred arrangement,the illumination reflecting means and the image conveying meanscomprises a common reflector element mounted for rotation to effect ascanning of the original document. Thus, the concentrated illuminationsource and the reflected image are inherently synchronized in thismanner thereby achieving a much more efficient imaging process than hasheretofore been attainable. Auxiliary means are provided in theillumination housing to further concentrate the light rays from thesource in the manner described. In an alternative version, separatemirrors are moved in synchronism.

2 OBJECTS Accordingly, a primary object of the present invention is toprovide an electrophotographic system with a highly efficientillumination and document scanning facility.

Another object of the invention is to provide a concentratedillumination and synchronized scanning system for electrophotographicapparatus.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiments of the invention as illustratedin the accom panying drawings.

DRAWINGS In the drawings:

FIG. 11 is a schematic diagram of a high speed copier system utilizing aphotoconductive belt for the conveyance of images produced thereon froman original document.

FIGS. 2 and 3, along with FIG. 4, illustrate an illumination source andlight concentrating facility for the system of FIG. 1.

FIG. 5 shows a unitary rotating reflecting mirror useful in the systemof FIG. 1, while FIG. 6 shows two rotating reflecting mirrors as analternative configuration.

FIG. 7 is a schematic representation of the optical system of theelectrophotographic apparatus with the document scanning andillumination mirrors removed.

FIGS. 8 and 9 are more complete versions of the illumination andscanning facilities utilizing the unitary reflecting mirror of FIG. 5and the two mirrors of FIG. 6, respectively.

DETAILED DESCRIPTION The High Speed Copier System FIG. 1 illustrates ahigh speed copier 'unit 101 incorporating the present invention. Theunit includes a photoconductor belt 102 and having a main frame 103supporting various elements for producing a multitude of copies at highspeeds from original documents. An original is positioned on theoriginal document plane 105 and illuminated by a lamp 106 in timedrelation with movement of belt 102. An optical system including mirrors110 and Ill and lens element 112 project the image of the originaltoward an image plane 102a on belt 102.

The unit in FIG. I has the customary electrophotographic stations andfacilities for producing copies. These include a cleaning brush 115 withassociated cyclone cleaning system 116, a charge corona station 118, theimage plane 102a, previously mentioned, a developer station 120, atransfer station 122, and a preclean corona station 123. Belt 102 ismounted for movement as indicated by arrow on drum driving elements 127and 128. A paper supply 130 accommodates a large quantity of individualsheets of paper that are fed by various devices including a belt 131 tothe transfer station 122 for transfer of images in timed relation withmovement of belt 102. Following such transfer, the image is fused byfuser 133, passes by transportation means 134, not shown, to acompletion station, such as a sorter copy bin 135.

The Illumination and Projection System The photoconductor imagingprocess is achieved by illuminating only the portion of the documentwhich is scanned during this process. Since the scanned area is onlyabout l/lO the total area of the document, the amount of illuminationrequired may be greatly reduced.

The method used to illuminate the portion of the document being scannedwill now be discussed with reference to FIGS. 2, 3, and 4. The source ofillumination will first be considered an idealized line source locatedat one of the foci of an elliptical reflector, that is, a part havingreflective surfaces 11 following a portion of elliptical curve 12 whichis perpendicular to line source 10. FIGS. 2 and 3 show this reflectorcut in the plane of ellipse 12. A pair of flat end reflectors havingreflective surfaces 13 perpendicular to the line source are placed ateither end of the elliptical reflector.

Due to the nature of the ellipse, any ray l4 emanated from the linesource at point 10a in the plane of ellipse 12 striking reflectivesurface 11 will be reflected to point 15a, the other focus of theellipse. It will now be shown that all rays emanating from the linesource and striking the reflective surface of the elliptical reflectorwill be reflected through line 15, the extension of this focus. Consideranother ray l6 emanating from point 10a at the same angle 17 as shown inFIG. 3, but at a different angle in a'plane perpendicular to that shownin this figure. Thus, rays 14 and 16 both strike the reflective surfacewhere its normal is defined by the plane shown with lines 18, the edgeof which appears in FIG. 3. By the law of reflection, the angle ofreflection as seen in FIG. 3 with respect to this plane remains as itwas for ray 14, that is, angle 19. Thus, the reflected ray also travelsalong the plane established by line 20 in FIG. 3, striking line 15 atpoint 15b.

Now consider another ray 21 emanating from point 10a at the same angle17 shown in FIG. 3. After reflection off the elliptical reflector, thisray also travels in the plane established by line 20 in FIG. 3, strikingend reflective surface 13. This plane is perpendicular to thisreflective surface. If this plane is viewed from its edge in thedirection of arrow 22, it can be seen that the angle of incidence withrespect to a normal drawn on this plane is zero. The angle of reflectionis therefore also zero as thus viewed, so the reflected ray remains inthis plane, striking line 15 at point 15c.

Because point 10a and angle 17 were arbitrarily chosen, it can be seenthat any ray emanating from line source 10 and striking reflectivesurface 11 is reflected through line 15.

FIG. 4 is a top elevation of the system, that is, a view taken in thedirection shown by section lines 4-4 in FIG. 2. FIG. 4 shows severalrays emanating from point 10a in a plane established by angle 23. Theray emanated vertically from point 10a is reflected to point 15a of line15. The ray emanating backward horizontally in this view is reflected atangle 24, which is equal to angle 23, to strike line 15 at point 15d.The other rays are reflected to cross line 15 at points 15e, 15f, and15g. Any point 10a of the idealized line source emanates light of equalintensity at all angles 17 and of varying intensity at all angles 23.Thus, any point on the line source illuminates all points on line 15with varying intensities. If the distance between lines 10 and 15 issufficiently great, relatively constant illumination may be obtainedalong line 15 when the line source at 10 is replaced by a series oflighted segments. This is important because the total width to beilluminated along line 15 is much greater than the filament length of anefficient tungsten lamp which could be used for document illumination.It is also possible to place lighted segments near the ends of line 10to help compensate for light losses inherent in the lens systems used incopying machines.

Although the illumination from an ideal line source as described isfocused on line 15, the illumination from any real source is spread overan area in the vicinity of line 15. Depending on the geometry of thelight source and the reflector, this area can be great enough to includethe area scanned by the copying process. The document to be copied mayotherwise be placed at some distance from line 15 to increase theilluminated area.

In the proposed illumination system, light from the reflector systemdescribed in the preceding paragraphs is deflected to follow thedocument scanning by means of a rotating flat mirror. The angulardeflection of light by such a mirror will now be discussed withreference to FIG. 5. Consider a light ray 25 striking reflective surface26 at the pivot point of rotating mirror 26a and at an angle 27 withrespect to the plane of the mirror. By the law of reflection, this rayis reflected as ray 28 at the same angle 27 as shown. Now consider themirror rotated through angle 29. Ray 25 now strikes the mirror at angle30 with respect to its plane and is reflected as ray 32 at the sameangle as shown. Thus, the rotation of the mirror deflects the reflectedray from its original position through angle 31. From the drawing, itcan be seen that:

(angle 30) (angle 27) (angle 29), and

(angle 31 (angle29) (angle 30) (angle 27) Substituting the firstequation into the second, it can be seen that:

(angle 31 2(angle 29) Now consider another ray 25 parallel to ray 25striking the mirror in its original position at point 26b at the sameangle 27 and reflected as ray 28' at the same angle 27. After the mirroris rotated through angle 29, this ray strikes the reflective surface ata new point 26c at the angle 30 as before and is reflected back at thisangle as ray 32'. Since the angles of reflection are the same as thoseachieved with ray 25, ray 28' is parallel to ray 28 and ray 32 isparallel to ray 32. Therefore, the motion of the mirror through angle 29deflects ray 32' through the same angle 31 which is equal to twice angle29.

In .the illumination systems proposed herein, the document isilluminated from the elliptical reflector system by means of a flatillumination mirror rotating with the flat document scanning mirror. Itwill now be shown that, when the following conditions are met:

1. The two mirrors rotate together (as a solid part) about an axis inwhich the planes of their reflectors intersect, and,

2. the illumination mirror and the illumination source are spaced in arelationship so that at a given point, such as the start of the scanningoperation, the area illuminated is the area scanned,

the following results are obtained:

1. The illuminated area will follow the scanned area on the surface ofthe document curved into an arc of a circle having its center at theaxis of rotation of the mirrors,

. the length of the light path from the illumination source to theilluminated document area will remain constant during the scanningprocess,

3. the length of the light path from the illuminated document area tothe lens will remain constant during the scanning process, and

4. the angle between these light paths measured at the document willremain constant during the scanning process.

FIG. 6 shows a pair of mirrors 35 and 36 rotated through angle 37 aboutan axis at 35a, the intersection of the planes of their reflectors.Consider a light ray 38 reflected from point 35a at angle 39 withrespect to the plane of reflector 35. Consider another ray 40 reflectedfrom point 36a at angle 41 with respect to the plane of reflector 36, sothat the reflection of this ray crosses the reflection of ray 38 atpoint 42. It has been shown in reference to FIG. 5 that when the mirrorsare rotated through angle 37, the reflections of both these rays will bedeflected through angle 43, which is twice angle 37, to cross at point44. Consider the triangle formed by points 42, 45, and 46 and thetriangle formed by points 44, 35a, and 46. Since these triangles agreein two angles, 43 and 47, they are similar, and the remaining anglesmust be equal. Therefore, the reflections of the rays cross at the sameangle 48 for both mirror positions.

Now consider a line drawn from point 35a at angle 37 with respect to theposition of reflector 36 after it has been rotated through angle 37.This line crosses the reflection of ray 40 to point 44 at point 49. Dueto the law of reflection, the angle 50 of ray 40 with respect to theplane of reflector 36 in this position is repeated in the triangleformed by points 36b, 35a, and 49. This triangle and that formed bypoints 36b, 35a, and 36a are alike in two angles, 37 and 50, and theyshare a common side, the line fromv 36b to 35a; so they are congruent.

Consider the triangle formed by points 51, 36a, and 35a. The angle ofthis triangle at point 35a is twice angle 37, which is equal to angle 43as shown in reference to FIG. 5. This triangle has another angle 52equal to the corresponding angle in the triangle formed by points 51,49, and 45. Since these triangles agree in two angles, they are similar.Therefore angle 53 is equal to angle 41.

Because the triangle formed by points 36b, 35a, and 49 is congruent tothe triangle formed by points 36b, 35a, and 36a; the line between points49 and 35a is equal in length to the line between points 360 and 35a.

The triangle formed by points 36a, 35a, and 42 therefore agrees with thetriangle formed by points 49, 35a, and 44 in one side and two angles, sothese triangles are congruent. The length of the line between points 42and 35a is therefore equal to the length of the line between points 44and 35a, so the point at which the reflected rays cross travels in anarc of a circle with its center at 350 as the mirrors are rotated.

Now consider the light path distance between a point 400 on the lines oflight ray 40 and the points at which the rays cross, 42 and 44. When themirrors are in their original position, this distance is equal to thesum of the lengths of the lines between points 40a and 36b, between 36band 36a, and between 36a and 42. When the mirrors are rotated throughangle 37, this distance is equal to the sum of the lengths of the linesbetween points 400 and 36b, between 36b and 49, and between 49 and 44.However, due to the congruence of the triangle formed by points 36b,35a, and 36a, with the triangle formed by points 36b, 35a, and 49, thelength of the line between points 36b and 36a is equal to that of theline between points 36b and 49. Also, due to the congruence of thetriangle formed by points 360, 35a, and 42 with the triangle formed bypoints 49, 35a, and 44, the length of the line between points 36a and 42is equal to that of the line between points 49 and 44. Therefore, thelight path distance from point 40a to the crossing point remainsconstant as the mirrors are rotated.

To this point, the discussion has considered a special case in which oneof the rays was reflected from the axis of rotation of the mirrors. Nowconsider another ray 54 reflected at point 35b of reflector 35 in itsoriginal position and oriented to cross the other rays at point 42. Theextension of reflector 35 to accommodate this ray may be considered aspecial case of the use of a separate reflector, such as reflector 36,with the angle between the reflectors equal to zero. The results shownfor the crossing of the reflections of rays 40 and 38 must also applyfor the crossing of the reflections of rays 54 and 38. That is, thereflection of ray 54 must also pass through point 44 after the rotationof the mirrors, the angle between the reflection of this ray and that ofray 38 must remain constant as shown by angle 55 during the rotation ofthe mirrors, and the light path distance from a point 54a on the line ofray 54 must remain constant during the rotation of the mirrors.Therefore, the total angle 55a between the reflections of rays 40 and 54must remain constant.

Now imagine an illumination source placed at point 400 and directedalong the line of ray 40 and a copying machine lens oriented to focusreflected rays, such as 54 on a photoconductive surface. The document tobe copied is placed in an arc of a circle centered at point 35a passingthrough points 42 and 44. With this configuration, the illuminated areawill follow the scanned area on the surface of the document, and duringthe scanning operation the length of the light path from theillumination source to the illuminated document will remain constant,the length of the light path from the illuminated document area to thelens will remain constant, and the angle between these light paths willremain constant.

The illumination source placed at 40a was arbitrarily located except forthe condition that the reflection of its illumination crossed the lightpath back through the lens at the document area scanned. The intensityof illumination may be increased by directing several illuminationsources toward the illumination mirror meeting this condition.Similarly, several responsive elements, such as lenses and light sensorsmay be directed toward the scanning mirror meeting this condition. Ifrequired, several mirrors may be arranged so the planes of theirreflectors all pass through the axis of rotation.

It is necessary that the light path from the scanned document area tothe lens remain constant to keep this area in focus. FIG. 7 shows why itis alsonecessary that the length of the light path from the illuminationsource to the illuminated document area remain constant. This figureshows schematically the optical system of the copying machine with thedocument scanning and illumination mirrors removed. Reflector 56concentrates light from lamp 57 on an area of document 58 centered atline 58a. End reflectors 59 are also used as previously described.Reflected light from the document passes through lens assembly 60 andthrough slot 61a in aperture plate 61 to the photoconductor drum (notshown) which is located a short distance beyond the aperture plate.

Without considering the aperture plate, when a white document is used,reflector 56 produces a relative illumination profile on the exposedphotoconductor area as shown by dashed lines 62. However, due to thenature of the optical system, for constant illumination of an area aboutline 580, the illumination on the photoconductor drum at an arbitrarypoint 63 is proportional to the fourth power of the cosine of angle 64.

In other words, the amplitude of the relative illumination curves varieswith this factor. The width of aperture slot 610 is increased as eitherof its ends is approached to compensate for this variation. The edges ofthis slot truncate the relative illumination curve so that a constantarea is obtained under this curve for each arbitrary position 63.

If the length of the light path from the illumination source to theilluminated area of the document were allowed to vary during thescanning process, the ability of reflector 56 to concentrate light inthe illuminated area would change with this variation. Thus, the amountof light passing through areas defined by the width of slot 61a wouldchange during the scanning process. A variation in the angle betweenthis light path and the path back through the lens to the photoconductorwould also change the amount of illumination seen at the photoconductor.

FIG. 8 shows one of the configurations of the illumination systemproposed in this disclosure. Light from lamp 65 is concentrated byelliptical reflector 66 and directed to area 67 by illumination mirror68 at the beginning of the scanning operation. Light from area 67 isdiffusely reflected back through lens assembly 69 by means ofillumination mirror 70. During the scanning operation, these mirrorsrotate together through angle 71 about an axis at 70a rotating theilluminated and scanned area through angle 72, which is twice angle 71.

The axis of rotation for the mirrors is shown at the center of the areaused for scanning. However, since the mirrors lie in the same plane,intersecting at all points in this plane, the axis may alternately beplaced elsewhere in this plane.

The possible presence of dust on the illumination mirror presents apotential problem referred to as flare. Since the intensity of lightstriking the illumination mirror is much greater than that striking thedocument scanning mirror, dust particles on the illumination mirrorcould direct scattered light back through the lens, affecting thephotoconductor imaging. A flare shield 73 is placed on the rotatingmirror assembly as shown to prevent this possibility. This opaque shieldblocks light that might travel from the illuminated surface of theillumination mirror through the lens.

End reflectors 74 are used as previously described.

To prevent ,the accumulation of dust on the mirrors and on the lens,this portion of the optical system may be sealed by the use of covers76, 77, and 78 and by the curved glass document platen 79. Theelliptical reflector may then be cooled by blowing air along its flns66a. An insulating heat shield 80 is included to reduce the radiation ofheat to the lens assembly. If it is necessary to cool the lamp itself, aglass plate 81 may be placed in front of the reflector as shown. Air isthen blown along the lamp and the reflective surface of the reflectorfrom one end to the other. This glass plate may also be used to absorbinfrared energy, reducing the temperature of the rest of the chambershown.

FIG. 9 shows an alternate configuration, with illumination mirror 82 anddocument scanning mirror 83 rotating through angle 84 about an axis at85, the intersection of the planes of their reflectors. An opaque shield86 is rotated with these mirrors to keep stray light from lamp 87 andreflector 88 away from lens assembly 89. This configuration is otherwisesimilar to that shown in FIG. 8, with a curved glass document platen 90forming an arc of a circle centered at axis 85, with end reflectors 91,with covers 92 and 93 sealing the optical chamber, and with a glassplate 94. Lens assembly 89 is tilted so that its optical centerline isperpendicular to the surface of the document on platen 90 as reflectedfrom mirror 83. As an example, lens 89 may, in a typical case, be tilted5 with respect to line 96 to establish this relationship. In otherwords, angle 93 between the centerline of the reflected image and thecenter of the curved document surface at equals angle 98 through whichthe lens is tilted relative to the reflection of the center of thescanned area.

While the invention has been particularly shown and described withreference to several embodiments, it will be understood by those skilledin the art that various changes in form and detail may be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:

l. Electrophotographic apparatus having facilities for scanningoperations with respect to an original document in order to producecopies from said document, comprising:

means for supporting said original document on a curved surface forscanning;

a rotating reflector element having planar reflective surfaces saidrotating reflector element comprising a pair of mirrors, one of saidmirrors serving as an illumination mirror, and the other of said mirrorsserving as a light reflecting mirror;

means mounting said mirrors for independent but synchronized scanningrotation within a predetermined range of scanning and about an axis thatis in parallel with respect to said curved surface for the transmissionof light and image information, said axis of rotation being arranged sothat a constant predetermined distance is maintained between said axisand said curved surface throughout a scanning operation;

a primary source of illumination;

means supporting said primary source of illumination for direction oflight rays emanating therefrom toward said illumination mirror forreflection from said illumination mirror to said original document;

a lens element;

means to project light rays from said source to said document andreceive reflections from said document for conveyance to said lenselement for imaging purposes comprising means positioning said lenselement in light conveying relationship with respect to said lightreflecting mirror, said lens element being oppositely positioned withrespect to said light source to form a generally symmetrical arrangementin relation to the axis of rotation of said reflector element, thearrangement being such that light from said light source is projectedalong a first light path of constant length to said reflector element,thence to said original document and at a first angle junctured at saidaxis of rotation, and image information from said document is reflectedthereafter along a second light path of constant length back to saidrotating reflector element and thence through said lens element to animaging area and at a second angle junctured at said axis of rotationthat is equal to said first angle, said first and second anglescombining to form an angle junctured along said curved surface thatremains constant throughout scanning operations; and

means for driving said rotating reflector element in timed relation toscan said original document for imaging purposes, thereby illuminatingthe area scanned on said original document throughout the scanningoperation with a light path of constant length from said document areato said lens, as well as maintaining constant the first and secondangles of said light paths with respect to said axis of rotationthroughout the entire range of scanning.

2. The apparatus of claim 1, wherein said mirrors are mounted toestablish congruent triangular light transmission paths throughout therange of scanning of said mirror elements to insure that the light pathtravelled from said source to said lens element remains constantthroughout scanning.

1. Electrophotographic apparatus having facilities for scanningoperations with respect to an original document in order to producecopies from said document, comprising: means for supporting saidoriginal document on a curved surface for scanning; a rotating reflectorelement having planar reflective surfaces said rotating reflectorelement comprising a pair of mirrors, one of said mirrors serving as anillumination mirror, and the other of said mirrors serving as a lightreflecting mirror; means mounting said mirrors for independent butsynchronized scanning rotation within a predetermined range of scanningand about an axis that is in parallel With respect to said curvedsurface for the transmission of light and image information, said axisof rotation being arranged so that a constant predetermined distance ismaintained between said axis and said curved surface throughout ascanning operation; a primary source of illumination; means supportingsaid primary source of illumination for direction of light raysemanating therefrom toward said illumination mirror for reflection fromsaid illumination mirror to said original document; a lens element;means to project light rays from said source to said document andreceive reflections from said document for conveyance to said lenselement for imaging purposes comprising means positioning said lenselement in light conveying relationship with respect to said lightreflecting mirror, said lens element being oppositely positioned withrespect to said light source to form a generally symmetrical arrangementin relation to the axis of rotation of said reflector element, thearrangement being such that light from said light source is projectedalong a first light path of constant length to said reflector element,thence to said original document and at a first angle junctured at saidaxis of rotation, and image information from said document is reflectedthereafter along a second light path of constant length back to saidrotating reflector element and thence through said lens element to animaging area and at a second angle junctured at said axis of rotationthat is equal to said first angle, said first and second anglescombining to form an angle junctured along said curved surface thatremains constant throughout scanning operations; and means for drivingsaid rotating reflector element in timed relation to scan said originaldocument for imaging purposes, thereby illuminating the area scanned onsaid original document throughout the scanning operation with a lightpath of constant length from said document area to said lens, as well asmaintaining constant the first and second angles of said light pathswith respect to said axis of rotation throughout the entire range ofscanning.
 1. Electrophotographic apparatus having facilities forscanning operations with respect to an original document in order toproduce copies from said document, comprising: means for supporting saidoriginal document on a curved surface for scanning; a rotating reflectorelement having planar reflective surfaces said rotating reflectorelement comprising a pair of mirrors, one of said mirrors serving as anillumination mirror, and the other of said mirrors serving as a lightreflecting mirror; means mounting said mirrors for independent butsynchronized scanning rotation within a predetermined range of scanningand about an axis that is in parallel With respect to said curvedsurface for the transmission of light and image information, said axisof rotation being arranged so that a constant predetermined distance ismaintained between said axis and said curved surface throughout ascanning operation; a primary source of illumination; means supportingsaid primary source of illumination for direction of light raysemanating therefrom toward said illumination mirror for reflection fromsaid illumination mirror to said original document; a lens element;means to project light rays from said source to said document andreceive reflections from said document for conveyance to said lenselement for imaging purposes comprising means positioning said lenselement in light conveying relationship with respect to said lightreflecting mirror, said lens element being oppositely positioned withrespect to said light source to form a generally symmetrical arrangementin relation to the axis of rotation of said reflector element, thearrangement being such that light from said light source is projectedalong a first light path of constant length to said reflector element,thence to said original document and at a first angle junctured at saidaxis of rotation, and image information from said document is reflectedthereafter along a second light path of constant length back to saidrotating reflector element and thence through said lens element to animaging area and at a second angle junctured at said axis of rotationthat is equal to said first angle, said first and second anglescombining to form an angle junctured along said curved surface thatremains constant throughout scanning operations; and means for drivingsaid rotating reflector element in timed relation to scan said originaldocument for imaging purposes, thereby illuminating the area scanned onsaid original document throughout the scanning operation with a lightpath of constant length from said document area to said lens, as well asmaintaining constant the first and second angles of said light pathswith respect to said axis of rotation throughout the entire range ofscanning.